1. Field of the Invention
This invention relates to a shaft coupling for transmitting torque from a drive shaft to a driven shaft. More particularly, the invention relates to a shaft coupling which has a joint element having two cylinders, one on each side of the coupling, for inserting the two shafts, two rings for radially tightening the tapering cylindrical parts, and set bolts for tightening the rings in the axial direction.
2. Description of the Prior Art and Problems Thereof
A prior art shaft coupling for connecting a drive shaft with a driven shaft by clamping a clamping ring in the axial direction has been already proposed in Japanese Patent Publication (examined) No. 59-48886.
The shaft coupling in this prior art, as shown in FIG. 7, comprises a joint element and two rings (2). The joint element has tapering cylindrical parts (11) formed on both sides thereof.
Under such construction, the clamping rings (2) are tightened by a plurality of set bolts (3), (3) in the axial direction (toward the large diameter portion of the tapered surface). In the connected state in which shafts D.sub.1 and D.sub.2 are inserted into the cylindrical parts (11,11), the rings are drawn together due to the tightening force applied by the set bolts 3 whereby the inner surfaces (2, 2) of the rings radially tighten the cylindrical parts.
According to this prior art, the cylindrical part (11) is in contact with the whole outer periphery of the shaft (D) and a torque is transmitted from the shaft to the shaft coupling by frictional force due to the clamping force produced in this cylindrical part (11). As a result, disadvantages such as eccentricity or backlash which are apt to occur while using a coupling structure including a key or pin can be overcome.
According to this prior art, however, the greater part of the torque transmitted from the drive shaft to the driven shaft is supported only by the cylindrical parts and a portion connecting the cylindrical parts. The cylindrical parts 11 must be elastically bent inwardly in order to tighten the shafts D. Therefor, a large torsional rigidity cannot be given to the parts 11, which reduces the torque load that can be transmitted therethrough and increases the likelihood that the parts will be damaged during use.